Organocatalytic [4+2] Benzannulation Between 1,4‐Dithiane‐Based Enal and Nitroolefins to Access 2‐Nitrobiaryls

A simple method for constructing unsymmetrical 2‐nitrobiaryls has been developed between substituted 1,4‐dithiine‐2‐carbaldehyde and nitroolefins under metal‐free conditions. To gain the advantage of the HOMO‐raising effect of temporary substitutions on in situ generated dienamine intermediate, the present protocol established [4+2] benzannulation of 1,4‐dithiane‐tethered enals with nitroolefin. Further, easy unmasking of 1,4‐dithiine units results in a benzannulation product like that of unsubstituted enals, which are difficult to access. Several 2‐nitrobiaryls have been accessed with moderate to good yields and with promising synthetic applications.